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A Review of the Utility of SPYBALs

Many times users want to know how long they can observe without a spectrum
Y-balance (SPYBAL) in an effort to limit the motion of the carrousel during
an observation. This report discusses the rationale for SPYBALS in terms of
the drift of the spectrum across the photocathode with time, taking into
account the tilt of the spectrum across the diode array. The results of
our investigation reconfirm that the default schedule of SPYBALs should be
used to keep the spectrum properly centered on the diode array.